The use of lactic acid bacteria as a post-harvest intervention to control escherichia coli O157:H7 in fresh spinach

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2008-12

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Abstract

In recent years, fresh spinach has been identified as a vehicle for Escherichia coli (E. coli) O157:H7 transmission. Multiple studies have demonstrated the ability of lactic acid producing bacteria (LAB) to reduce the presence of Escherichia coli O157:H7 in food products and the efficacy of LAB cultures as a post – harvest intervention in fresh spinach production should be evaluated. To determine the effect of spinach inoculated with Escherichia coli O157:H7, spinach samples were rinsed with sterile distilled water and a four – strain LAB cocktail at a target concentration of 2.0x108 CFU/mL. Both treatments were compared to an inoculated control over a 24 – hour time period at 7oC. According to composite LS means data obtained for each treatment, water and LAB resulted in significant reductions of 0.88 logs (p<0.0001) and 1.03 logs (p<0.0001) in comparison to the control, respectively. The improved reduction of LAB was significantly better than that of water (p=0.0363), making it the most effective treatment.

A triangle test was conducted to determine if a statistically significant difference in sensory characteristics exists when LAB is applied to fresh spinach. Two samples were rinsed with tap water and considered to be identical. The remaining sample was rinsed with LAB at a concentration of 2.0x108 CFU/mL. 40 panelists participated in the test and 16 correctly identified the LAB – treated spinach as being the one unique sample. These results indicate that a statistically significant difference does not exist (á=0.05, 0.01) when LAB is applied to fresh spinach and that the use of LAB may be acceptable from a consumer acceptance standpoint. The ability of LAB to control E. coli O157:H7 populations in combination with the industry standard chlorine rinse was determined in a 12 day shelf – life study at 7oC. The multi – hurdle intervention was evaluated in comparison to water, LAB and chlorine rinses. LAB cultures were applied at a concentration of 2.0x108 CFU/mL, while chlorine was utilized at the 200 ppm level. As indicated by composite LS means data, significant reductions in comparison to control populations were achieved by the LAB (p=0.0215), chlorine (p=0.0002) and multi – hurdle treatments (p<0.0001). However, the multi – hurdle treatment produced the greatest reductions with 1.35 logs. This reduction was significantly improved upon LAB (p=0.0012) and chlorine (p=0.0815), indicating that the application of chlorine and LAB is most effective as a combination treatment.

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